Leclanche type galvanic dry cell batteries have long been used as the energy source of choice in portable electronic equipment including flashlights, toys, radios, audiocassette and compact disc players, and other devices. An inherent disadvantage of such batteries, however, is their tendency to leak the cell exudate, which is a by-product of the electrochemical reaction by which the dry cells generate electrical energy. As is known, such leakage may result in premature discharge of the cell's stored energy. In addition, because of its highly corrosive nature, dry cell exudate leakage may result in irreversible damage to metallic exterior components of the battery itself or, more importantly, the equipment with which the battery may be used.
Carbon zinc Leclanche dry cells have largely been abandoned by consumers in favor of more expensive, powerful and reliable alkaline batteries. Battery manufacturers have also disfavored carbon zinc designs because of the numerous bulky layers which comprise the cover which encases the dry cell as well as the problems associated with the leakage of corrosive exudate from such batteries. However, because carbon zinc dry cells are less expensive to manufacture than their alkaline counterparts and because many applications do not require the longer service life of alkaline cells, carbon zinc batteries are again becoming attractive alternatives in the marketplace.
More recent designs of carbon zinc batteries comprise a zinc outer casing rather than traditional cardboard casings which were particularly susceptible to leakage. Although zinc casings have reduced the amount of leakage from the cell, such casings have not eliminated leakage and have introduced certain structural problems. While the battery is in use, the carbon contained in the cell reacts with the zinc of the outer casing such that the zinc is consumed in the electrochemical process to produce electrical energy and zinc chloride is produced as a by-product. Over time, the electrochemical process consumes the zinc of the outer casing to the point where the thickness of outer wall is reduced. As the outer casing becomes thinner, the cell becomes more susceptible to zinc chloride and other exudate leakage as well as structural weakening of the cell itself.
Moreover, the exudate tends to react with and destroy pressure sensitive adhesive labels of standard construction which, in some dry cells, are applied to the external surface of the outer casing of the battery.
It has long been accepted in the alkaline battery and pressure sensitive labeling arts that a layer of shrink PVC must be used as the base layer of two-ply pressure sensitive adhesive labels. In this regard, a typical alkaline battery label construction comprises a base layer of polyvinyl chloride ("PVC") which shrinks approximately 45 to 55% in relation to its original size when heat is applied to the PVC, and a second outer layer of blown fiber PVC film. The facing surfaces of the two layers are bonded together via lamination techniques known in the art. Adhesive is applied to the exposed surface of the base layer in order to allow the labels to be adhered to the outer surface of the cell.
Although this sort of label construction is compatible with alkaline batteries, it cannot be used with carbon zinc batteries primarily because the base layer of shrinkable PVC cannot contain the cell exudate. Consequently, the two-ply PVC label of the type described above has been largely ignored as an alternative for carbon zinc batteries.
Accordingly, there exists a need for an inexpensive method and apparatus for (1) resisting exudate leakage from a carbon zinc battery cell, (2) protecting and supporting the cell structure as the outer zinc casing deteriorates over the cell's useful life and (3) providing aesthetically pleasing and durable indicia bearing surfaces for application of manufacturer's logos, instructions, and other information, many of which have relied on rigid outer casings of paper, metal and plastic.
Many proposals have been offered to counter the problem of dry cell battery exudate leakage. In U.S. Pat. No. 3,223,557 for example, the dry cell is disclosed as being encased within an oversized, loose-fitting, paper and plastic jacket defining a chamber between the body of the dry cell and the jacket. The purpose of the chamber is to collect and retain cell leakage. Even if absolutely effective in preventing leakage of liquid exudate, the bulkiness and loose fit of the jacket is undesirable.
First, the jacket adds undesirable size to the battery construction. To assure compatibility with most electrical equipment, dry cell batteries must assume standardized sizes, e.g., from AAA to D. Hence, in a dry cell battery constructed according to that described in U.S. Pat. No. 3,223,557 the outer dimensions of the protective jacket must correspond to such standardized sizes. In doing so, however, the actual size of the enclosed dry cell itself is compromised since there must also be provision of the aforementioned leakage retention chamber between the jacket and the dry cell. Consequently, a net reduction in the size of the dry cell reduces the volume of chemical material available to the cell for producing electrical energy, thereby reducing the power output and service life of the battery.
In addition, the loose fit of the jacket about the body of the dry cell also permits distortion and crushing of the jacket which may result in breakage to the jacket's seal and/or damage to the dry cell.
Somewhat more conventional dry cell enclosures are disclosed in U.S. Pat. Nos. 3,753,781 and 5,079,108. According to these designs, the dry cell is tightly encased within an insulator tube formed of cardboard or other suitable material which is closely surrounded by a metal or polymer coated paper jacket. Batteries of this sort have demonstrated varied degrees of success in resisting exteriorly applied impact stresses and containing cell exudate. In those batteries whose insulator is formed from cardboard or other fibrous material, the exudate leakage can readily saturate the insulator tube. And, if the protective outer jacket is made of metal, the exudate can corrode the jacket to a point where the exudate escapes from the jacket. Alternatively, if the outer jacket is constructed from polymer coated paper, the paper of the jacket may also become saturated thereby exposing the polymer to chemical attack. Moreover, as with the dry cell disclosed in U.S. Pat. No. 3,223,557, each of these constructions require bulky jackets to fit over the zinc anode can. Addition of these jackets not only decreases the amount of space available for the cell itself, it also adds numerous steps and additional cost to the manufacturing process. Each sleeve must also be manufactured to exacting specifications prior to assembly to assure that each component part fits together precisely.
U.S. Pat. No. 5,079,108 seeks to limit potential exudate leakage by enclosing substantially all or a portion of the dry cell in a combination of seal member of low moisture permeability, compression member and sealing means. The sealing means may be a thin walled adhesive plastic tape or a heat shrinkable wrap or tube. In this invention, the sealing means must cover all of the edge and at least a part of the upper surface of the sealing member. Moreover, a prefabricated insulator tube and paper jacket must slip over the dry cell and sealing means necessarily requiring the insulation tube and paper jacket must be fabricated to exacting tolerances prior to assembly. Consequently, the combination of these components complicates construction and adds to the manufacturing cost of the battery.
U.S. Pat. No. 5,026,616 describes a dry cell battery construction wherein the dry cell is enveloped by a single layer, electrically nonconductive jacket, such as an electroless plated plastic covers, which has an increased resistance to corrosion. The corrosion resistant jacket is prefabricated to precise tolerances. Moreover, there is no disclosure that the jacket itself may function as an aesthetically pleasing and durable indicia bearing surface without need for application of an additional label or outer coating.
U.S. Pat. Nos. 4,801,514, 4,911,994, 5,262,251, 5,312,712, 5,326,654, 5,358,804 and Canadian Patent No. 1,296,891 disclose multiple layer labels adapted for adhesive attachment to the outer circumferential surface of the protective jacket of a conventional Leclanche type dry cell battery. The multiple layer label constructions create a long-lasting and attractive indicia bearing surface about the circumference of the battery. The battery labels are formed from a plurality of very thin layers of stretchable plastic film, adhesives and indicia material. However, none of the structures disclosed provide for an inexpensive adhesive enclosure which is capable of resisting exudate leakage.